In other words, what is the similarity between a lightning bolt and a wobbling sheet that make them sound alike?

It seems to me that the two systems have a much different way of moving the air, and probably if you could hear it up close, a lightning bolt wouldn't make the sound of a wobbly metal sheet. I think maybe the many reflections and how they interact with the cylindrical shape of the thunder-wavefront may be what gives the similarity.

I suppose I would first want to know if the two sounds are actually similar in terms of waveform analysis. I agree that they sound similar to my ear, but perhaps this is just an artifact of human perception.
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Tim GoodmanAug 15 '12 at 21:46

That is a good point. I'm not sure how to reason about that aspect of the problem besides assuming it's a small effect and that the spectrum is indeed similar (at least in a certain range of frequencies, 20-20000Hz as is our hearing range).
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Ryan ThorngrenAug 15 '12 at 22:18

1 Answer
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With some experimentation, I've found that a sheet, when wobbled gently, makes a 'wub' sound which has a different spectrum than rolling thunder. However, when wobbled violently, the sheet forms bulges which narrow and sharpen and then suddenly flatten, making a loud 'blap' like a thunderclap. The reverberations in the sheet of this flattening seem to give the rolling effect of thunder.

Indeed, the sudden flattening looks like it creates a the sort of sharply single-peaked pressure wave I expect close to a lightning bolt. I asked a friend who lives where there is plenty of lightning, and he confirmed that close to lightning, there is no rolling thunder.

This suggests to me that there is a similarity between how the flattening reverberates in the sheet and how the thunderclap reverberates across a landscape.

EDIT: I don't think the sound comes from the whipping effect at the bottom of the sheet because a similar sound happens with an aluminum foil sheet, where the sound is definitely not coming from the whipping of the bottom, which doesn't get very fast with aluminum foil.